The current invention relates to medical stents in general, and specifically to intravascular bifurcation zone implants and crimping and deployment methods thereof. In the specification and claims which follow hereinbelow, the term “implant” is a general term, interchangeable with “intravascular device”—both terms herein intended to mean “stent-graft”—as known in the art. The terms “bifurcation zone” and “bifurcation”, and variations thereof, as used in the specification and claim which follow hereinbelow, are intended to mean points/places/zones in the vascular system where at least one secondary/side blood vessel branches out of a typically larger, main artery/blood vessel.
The term “delivery system”, as used in the specification and claims which follow hereinbelow, is intended to mean a catheter and associated components, used to deliver and deploy an implant. Part of the catheter is a tube, as known in the art. The term “sheath”, as used in the specification and claims which follow hereinbelow, is intended to mean a containment configuration/enclosure of one or more crimped stents. The sheath is included in the tube of the delivery system, as known in the art. Additional components of the delivery system include, but are not limited to: guide wires and other wire/activation mechanisms, typically included in the catheter. The catheter is characterized by a “distal end”, meaning the end of the catheter inserted into the body to the proximity of the bifurcation zone, and a “proximal end”, meaning the end of the catheter extending out of the body, from where the delivery system is activated/manipulated by a skilled individual. Typically, the sheath is located substantially at the distal end of the catheter.
The term “sub-procedure”, as used in the specification and claims which follow hereinbelow is intended to mean an initial insertion of a delivery system into a body and/or a singular reinsertion of a delivery system or components thereof, typically following previous withdrawal of the delivery system from the body—all as part of an overall procedure or operation. As such, the term sub-procedure is intended to mean and include a singular insertion and associated withdrawal of the delivery system or components thereof.
The term “chronology”, as used in the specification and claims which follow hereinbelow, in reference to an implant procedure, is intended to mean the overall time and/or sequence of sub-procedures involved in an implant procedure or operation. The duration and number of sub-procedures and/or their complexity contribute to longer chronology. Therefore, the term “chronology” is used interchangeably hereinbelow to additionally mean the sequence, relative complexity, and/or the number of sub-procedures involved in an implant procedure or operation. It is desirable to perform fewer and/or less time-consuming operations in a procedure—including the overall time and/or the number and/or sequence of operations. It is for this reason that shortening or lowering the chronology in an implant procedure is desirable.
A stent is placed or implanted within a vein, artery, or other tubular body organ, as known in the art, for treating an occlusion, stenosis, aneurysm, collapse, dissection, or weakened, diseased, or abnormally dilated vessel or vessel wall, inter alia, by expanding the vessel and/or by reinforcing the vessel wall. In particular, stents are quite commonly implanted into locations such as, but not limited to: coronary, cardiac, pulmonary, neurovascular, peripheral vascular, renal, gastrointestinal, and reproductive systems.
Two important currently-used applications for stents are directed to improving angioplasty results by preventing elastic recoil and remodeling of the vessel wall and for treating dissections in blood vessel walls caused by balloon angioplasty of coronary and peripheral arteries, by pressing together intimal flaps in the lumen at the site of a dissection. Conventional stents have been used with limited success rates for treating more complex vascular problems, such as lesions at or near bifurcation zones.
Conventional stent technology is relatively well-developed. Conventional stent designs typically feature a straight tubular-shape, single type cellular structure, configuration, or a pattern that is repetitive along the stent longitudinal axis. In many stent designs, the repeating structure, configuration, or pattern have strut and connecting-balloon catheter portions that can impede blood flow at bifurcations. In addition to various implant configurations addressing bifurcation stenting, there are many methods for delivering a stent at or near a bifurcation point, commonly called Fenestrated Endovascular Repair (FEVAR). The following are selected prior art addressing the problem.
Bourang, et al. in U.S. Pat. No. 9,737,424, whose disclosure is incorporated by reference, describe a crimping method that crimps a stent over multiple catheters. The method includes differentially crimping a stent on certain portions of a balloon catheter so that a second catheter can be threaded through the uncrimped portion of the stent and exit through the links of a conventional stent design or through a specific hole in the stent designed for a branched vessel.
In U.S. Pat. No. 9,730,821, whose disclosure is incorporated by reference, Bourang et al. describe a system for treating a bifurcation includes first and second delivery catheters, each having an expandable member. A stent having a side hole is disposed on the second delivery catheter. A portion of the first delivery catheter is disposed under a portion of the stent. The first delivery catheter is slidable relative to the second delivery catheter, and the first delivery catheter passes through the side hole. Expansion of the first expandable member expands a portion of the stent and expansion of the second expandable member expands the rest of the stent.
Pallazza, in U.S. Pat. No. 9,492,297, whose disclosure is incorporated by reference, describes an expandable medical balloon useful for treatment at a vessel bifurcation, the balloon having at least one expanded state, the balloon having at least one inner layer and at least one outer layer, the outer layer having at least one cavity therein through which the inner layer protrudes when the balloon is in its at least one expanded state, and methods of making and using the same.
In U.S. Pat. No. 9,610,182, whose disclosure is incorporated by reference, Douglas describes a system for treating disease involving branching vessels of a mammal system can include a main graft assembly (i) having a lumen permitting fluid flow therethrough, and (ii) configured to expand within a first vessel of a mammal; and a branch graft assembly including a branch cover (i) having a cover lumen permitting fluid flow therethrough; and (ii) configured to expand within a branch vessel that branches from the first vessel. The branch graft assembly may also include an expandable branch stent extending within the cover lumen. The branch graft assembly may further include a branch sheath (i) extending between the branch stent and the cover lumen, and (ii) constraining radial expansion of the branch stent within the cover lumen.
Feld et al., in U.S. Pat. No. 9,101,500, whose disclosure is incorporated by reference, describes methods and devices for placement of a stent in a bifurcation or ostial lesion. The stent comprises a main body and a flaring portion. The main body is designed to expand and support a main vessel of the bifurcation and defines a main body axis. The flaring portion is disposed on a side of the main body and is adapted to flare radially and offset the main body axis in response to expansion of the main body. The flaring portion comprises at least one distal wing and at least one proximal wing. Each wing is aligned along the main body axis. The at least one proximal wing is longer than the at least one distal wing, providing greater coverage of the proximal side of the side vessel than on the distal surface of the side vessel.
In U.S. Pat. No. 9,101,457, whose disclosure is incorporated by reference, Benary describes an endovascular stent-graft system, which includes fenestrated and crossing stent-grafts. The fenestrated stent-graft defines first and second lateral apertures in a central portion thereof, which apertures face in generally radially opposing directions. The crossing stent-graft includes one or more covering elements, which at least partially cover both end portions of the crossing stent-graft, such that a central portion is at least partially uncovered. Both stent-grafts are sized and shaped such that, when the crossing stent-graft is disposed through both apertures such that the central portion thereof is within the central portion of the fenestrated stent-graft, both end portions of the crossing stent-graft (a) pass through both apertures, respectively, and (b) when both stent-grafts are in radially-expanded states, form blood-impervious seals with both apertures, respectively.
Reference is currently made to FIG. 1A, which is a schematic view of a typical aortic renal zone having an endovascular aneurysm 3 and a prior art endovascular aneurysm repair (EVAR) implant 3. Prior art implant 3 is characterized by: a plurality of fixation of anchoring barbs 4; a main body 5; a contralateral gate 7; a contralateral limb extension 8; and an ipsilateral limb 9, in treatment of Abdominal Aortic Aneurysms (AAA)—all as known in the art
Reference is additionally made to FIGS. 1B-1E, which are schematic diagrams of respective morphologies of Infrarenal (1B), Juxtarenal (1C), Pararenal (1D), and Suprarenal (1E) AAA—as known in the art—showing variations (2b, 2c, 2d, 2e) of typical aortic renal zone configuration 2 of FIG. 1A. An “aortic neck” (also referred to hereinbelow as “neck”) is indicated by dimension “a”, shown in FIGS. 1B and 1C. In prior art Juxtarenal/Suprarenal AAA repair, the presence of an aortic neck is necessary to receive fixation barbs 3 (ref FIG. 1A), which are used to anchor the implant onto the neck and to prevent a Type I endoleak. As such, the variations of typical aortic renal zone configuration corresponding to Juxtarenal, Pararenal, and Suprarenal AAA's are increasingly difficult/improbable choices for such repairs.
EVAR repair typically takes advantage of FEVAR, as known the art. Prior art FEVAR can be broadly described as employing one of two well-known implant types, namely: off-the-shelf implants and custom-made implants. In both cases, the fenestrated portion of a main stent refers to integrated “lateral fenestrated apertures”: namely openings in a main stent, positioned to accommodate side-branching vessels and subsequent deployment and configuration of secondary (or “side”) stents therein. Most typically, at least two smaller-diameter stents are deployed after passing through the lateral fenestrated apertures to fit secondary arteries, which branch out of the typically larger, main artery. These “smaller diameter portions” are also referred to herein below as “side stents”—as opposed to the “main stent”. Representative steps in a typical FEVAR are presented hereinbelow.
Custom-made implants, as known in the art, which have heretofore been more prevalent for FEVAR, allow an optimal match to a specific bifurcation configuration and generally higher success rates. However custom-made implants have significant disadvantages such as, but not limited to: higher fabrication cost; and very long lead times to fabricate/fit the implant, as fabrication of custom-made implants involves time-consuming iterations between the manufacturer and physician, and the need for multiple CT scans of the patient—all additionally contributing to cost.
Off-the-shelf implants, on the other hand, generally address one or more “average” physiological bifurcation configurations—affording relatively lower fabrication cost and much quicker availability but not necessarily an optimal/custom fit—a point which is discussed further hereinbelow.
Some available off-the shelf implants, including the date of regulatory approval with CE mark for the European market, listed below according to EVAR and FEVAR, include:
EVAR                “Incraft”, by Johnson & Johnson, 2014, 1820 McCarthy Blvd., Milpitas, Calif. 95035, USA        “Vanguard”, by Boston Scientific, 2011, 300 Boston Scientific Way, Marlborough, Mass., 01752-1234, USA        “Excluder”, by W. L. Gore & Associates, 2013, 555 Papermilll Rd., Newark, Del. 19711, USA        “Altura”, by Lombard Medical, 2016, 4 Lombard Medical House, Trident Park, Didcot OX11 7HJ, UK        “Endurant II”, Medtronic, 2016, 20 Lower Hatch Street,        “Netlix”, 2013, and “Ovation”, 2014, Endologix, 2 Musick, Irvine, Calif. 92618, USA        
FEVAR                “Ventana™”, ENDOLOGIX, INC., 2 Musick, Irvine, Calif. 92618 U.S.A.        “Zenith® p-Branch® Endovascular Graft”, COOK MEDICAL LLC, P.O. Box 4195, Bloomington, Ind. 47402-4195, USA.        
Some available FEVAR custom-made implants include:                “Anaconda™”, Terumo Vaskutek, Newmains Avenue, Inchinnan, Renfrewshire, PA4 9RR, Scotland, UK        “Custom-made Zenith™”, COOK MEDICAL LLC, P.O. Box 4195, Bloomington, Ind. 47402-4195, USA.Limitations in Prior Art Implant Techniques        
Prior art implant techniques in bifurcation zones are limited by catheter flexibility and rigidity, which subsequently impact the rigidity and length of a crimped implant device inside the sheath of the catheter.
Another limitation in prior art branch side stents or main stent frame extensions is that they typically address bifurcation inclinations of less than 70 degrees relative to the central axis of the main vessel. In cases where bifurcation inclinations exceed 70 degrees (ie approaching the normal, meaning 90 degrees) implant techniques become excessively complicated—as the catheter and its payload would be subject to relatively sharp bending. In addition to mechanical limitations imposed by crimping on prior art stents, inclusion of excessively-crimped prior art stents, combined with relatively sharp bending of the catheter can lead to mechanical fatigue/failure of the stent and thus pose excessive risk in such procedures and/or over time.
In the specification and claims hereinbelow, the expression “inclination of at least 70 degrees with respect to the main blood vessel longitudinal axis” is intended to mean an angle approaching the normal to the main blood vessel longitudinal axis, namely 90 degrees.
An example of a prior art related to crimping of stents is Kheradvar et al., in U.S. Pat. No. 8,702,788, whose disclosure is incorporated by reference, describes an expandable stent that can transform between a collapsed state and an expanded state. The stent includes a first cross-sectional shape and a second cross-sectional shape. The first cross-sectional shape is a non-convex shape when the stent is in the collapsed state. Alternatively, the second cross-sectional shape is a convex shape when the stent is in an expanded state. The stent can be formed of super elastic Nitinol, which allows it to be shape set in the desired shape. Due to its shape setting properties and the non-convex cross-section, the stent is capable of dramatically reducing its cross-sectional radial profile which is beneficial in a variety of procedures.
In addition to the limitations noted above, when the implant is deployed (including the side stent) the overall, final implant configuration can be exposed to material fatigue, as the bifurcation angle predisposes the side stent to strut fracture. Additionally, any open areas between the main stent and the side stent following balloon dilatation can lead to thrombus and/or endoleaks, as known in the art.
A more complicated case presents itself when the ratio of the main vessel diameter to the secondary vessel diameter is greater than 2. In such a configuration, deployment of a side stent is typically more complicated, for reasons as noted hereinabove.
In other scenarios, such as in the carotid artery, in the Willis region (also known as “Circle of Willis”), blood flow must not be blocked during deployment of the implant from the catheter, as the organ fed by the secondary vessel (in this case, the brain) must receive blood during the procedure to maintain organ functionality. In renal artery-related procedures, blood flow may be temporarily limited, but only for short periods.
Implant producers are faced with formidable challenges to support all sizes/scales of vessels having variable amorphic geometries, varying from patient-to-patient—all in addition to addressing parameter changes, as discussed further hereinbelow.
Aortic renal zones represent an exemplary case of multi-parameter geometry varying among patients—including: scale variations of different diameters for the main aorta vessel and renal branch vessels; height differences between left and right renal arteries; and angular variations between renal vessels relative to the axis of the aorta in both radial and axial directions.
Representative Steps in a FEVAR Procedure
Representative steps in a FEVAR procedure using implants such as those indicated hereinabove are described by S. Oderich et al. in “Technical Aspects of Repair of Juxtarenal Abdominal Aortic Aneurysms using the Zenith Fenestrated Endovascular Atent Graft”, Journal of Vascular Surgery 2014; 59:1456-61, whose disclosure is incorporated by reference. Reference is currently made to FIGS. 2-6, which are schematic cross-sectional views of a typical aortic renal zone 10, showing a main artery 11 and steps in a Prior Art FEVAR procedure (suprarenal components only), as described by Oderich et al.
Current FEVAR and similar endovascular repair procedures are characterized by the following summarized steps:                1. Precathetization of target vessels 12 (ie renal arteries) is performed, passing guide wires 14 to the so-called “landing location”. The delivery system addresses complex vessel turns in typically narrow blood vessel channels—ref FIG. 2.        2. In FIG. 3, a catheter 20, including a crimped stent 21, is inserted. Stent fenestrations 22 are then aligned with the target vessels, by rotating the catheter, as indicated by the arrows. Typically, orientation of fenestrations 22 with regard to the guide wires is ascertained using imaging techniques. (Duplicate indicia, as indicated in FIG. 2, are not indicated in the current and following figures for purposes of clarity.)        3. Guide wires 14 are removed/withdrawn and then reintroduced, this time gaining accesses from within the fenestrated stent—ref FIG. 4.        4. In FIG. 5, stent 21 is deployed, including proximal balloon dilatation of the suprenal stent graft (ie stent 21) and catheter 20 (ie delivery system) is removed/withdrawn.        5. Balloon-expandable stents 25 are deployed into renal arteries 12, with proximal flaring of respective stents 25 performed with angioplasty ballooning.Additional Limitations and Risks in Prior Art Implant Techniques        
The multi-parameter geometry as described hereinabove calls for a corresponding multi-parameter solution. One solution known in the art is based upon multi-component implantation of an independent/main implant (for aorta and renal applications), which is subsequently connected by shrink fitting (stent-within-stent) to one or more branch stents after deployment—such as described by Oderich et al., hereinabove. Connection of the stent components takes place in an amorphic, native vessel geometry, which is influenced by regular, pulsating blood flow. Such a multi-component solution demands production of a dedicated delivery system for each component and a relatively long-chronology transcatheter surgery procedure. As noted in the description of FIGS. 2-6 hereinabove, such a transcatheter procedure requires multiple vessel entrances to allow ingress for guidewires and support equipment. In the case of the risk of aorta rupture based on the para-renal aneurysm, the multi-component transcatheter procedure described hereinabove may provide a solution, albeit a complicated one. Among the factors adding to risk from/following the procedure are:                migration of the stent-graft and side stents;        renal events (such as: renal artery stenosis, occlusions, and infarcts);        post-operative acute renal failure (ARF);        fatigue and fracture of the stent/stents;        ischemic strokes, in case of the complicated renal arteries angularity, and required manipulation of brachiocephalic vessels during side stent implantation; and        endoleaks following the procedure.        
Some factors adding to complexity in a procedure are:                long procedure time—ie long chronology—with a typical total operation time between 2 to 3 hours and fluoroscopy time between 50-70 minutes;        involvement of support equipment for a FEVAR procedure (such as: a multi-sheath introducer, a marker catheter, and dedicated post dilatation balloons); and        multiple renal artery approaches for complex angularity cases (such as through brachiocephalic and left subclavian arteries) with accompanying increased risk of an ischemic stroke.        
In addition to the risk and complexity elements noted hereinabove, the variation of different products from different vendors and of the deployment and fixation of each component in a procedure can contribute to unpredictability of functionality of a complete implant—again exacerbating overall cost and/or risk.
As observed in the procedures outlined above, off-the-shelf implants have integrated lateral fenestrated apertures not necessarily custom-fit to the patient. This constraint imposes a major impact on the chronology of the procedures—as repetitive sub-procedures and most careful attention must be given to attempt to align the lateral fenestrated apertures of the stent with a given patient morphology. There are a number of documented risks associated with off-the-shelf implants and deployment methods following Juxtarenal/Suprarenal AAAs Repair, as a part of FEVAR procedure, as presented hereinbelow:
A. Kitagawa et al., in an article entitled: “Zenith p-branch Standard Fenestrated Endovascular Graft for Juxtarenal Abdominal Aortic Aneurysms”, Society for Vascular Surgery, 2013—whose disclosure is incorporated by reference—indicates that the overall applicability of stent-graft was 72% for patient aneurysms. There is no description of success rate (usually relating to results of the procedure) as the article does not deal with any procedure results, but rather applicability of the stent graft.
R. K. Greenberg et al., in an article entitled: “Intermediate Results of a United States Multicenter Trial of Fenestrated Endograft Repair For Juxtarenal Abdominal Aortic Aneurysms”, J Vasc Surg for FEVAR, 2009, whose disclosure is incorporated by reference, notes that after FEVAR, based on the intermediate-term (24-month) results, up to 30% of the patients experienced a renal event (renal artery stenoses, occlusions, and infarcts).
In an article entitled: “Durability Of Branches In Branched And Fenestrated Endografts”, by T. M. Mastracci et al., 2013, J Vasc Surg, whose disclosure is incorporated by reference, it is indicated that based on the long-term clinical follow up, the maximal cause for reinterventions is caused by failure in the renal arteries (6% of right renal artery and 5% of left renal artery).
A final example is by T. Martin-Gonzalez et al., in an article entitled: “Renal Outcomes Following Fenestrated and Branched Endografting”, Eur J Vasc Endovasc Surg, 2015, whose disclosure is incorporated by reference. T. Martin-Gonzalez et al note that post-operative acute renal failure (ARF) was seen in 29% of patients with median follow up 3.1 years (2.9-3.3 years).
As such, it may be summarized that current prior art implant procedures have risks, complexity, and expenses, along with concomitant long procedural chronologies.
There is therefore a need for implant configurations and associated techniques that can allow additional/more effective crimping of stents to address aorta and bifurcation branches using a singular procedure and/or minimal sub-procedures, thereby yielding minimal and/or reduced chronology and having concomitant higher success rates (and/or lower risks) in the short and long run. Such implants and techniques would be especially beneficial for endovascular Juxtarenal, Pararenal, and Suprarenal Abdominal Aortic Aneurysm (AAA) and analogous Thoracic Aortic Aneurysm (TAA) procedures/repairs.